§ I EXAMINATION OF BITTERLING HYPOPHYSIS 55 



produce the sexual hormone (oviductin), which causes 

 growth of the ovipositor. 



b. Hypophysectomy and "faliing-off" phenomena. 

 If the above description of the process is correct, removal of 

 the hypophysis must result in "falling-off" phenomena. This 

 proved to be the case. 



Technique. After a search for the most suitable method of operation, 

 boring out the hypophysis with a dentist's drill from fishes under nar- 

 cosis proved to be most effective. The fishes u^ere narcotised v^ith ethyl- 

 urethane. The palata was sounded with a fine drill until resistance was 

 felt about i mm behind the posterior orbital wall, which indicated the 

 bony protuberance of the parasphenoid, protruding into the cavity of the 

 mouth. The hypophysis lies in a bend of this protuberance. The drill was 

 held slanting slightly upwards, drilling being done very carefully, for 

 about I mm in this direction. When placed back into fresh water the 

 fish recovered fairly quickly from the effects of narcosis. 



All the bitterlings treated were tested with a very active 

 hormone mixture (progesterone, desoxycorticosterone). The 

 majority of the fishes possessed extremely long ovipositors 

 after a 5 hours' test. On histological examination they proved 

 not to have been hypophysectomised, the majority having 

 been drilled too far anteriorly. One fish, however, which 

 showed no growth of the ovipositor, was found to have been 

 totally hypophysectomised. Histo-statistical examination 

 showed that the ovaries of those bitterlings in which the 

 hypophysis had not been removed completely, contained 

 numerous corpora lutea (between 42 % and 64 %), whereas 

 to ovary of the hypophysectomised individual contained only 

 a few old remains, not originating from this latest reaction.' 

 It is clear, therefore, that ( i ) without the pituitary no cor- 

 pora lutea are produced, and no growth of the ovipositor can 

 therefore result; (2) the reaction to progesterone and des- 

 oxycorticosterone must first come through the hypophysis, 

 and does not come direct from the gonads. From this latter 

 fact, which applies, in the bitterling, to all steroids examined, 

 it is clear that the reaction in the fish is the reverse of that 

 in mammals. In mammals, as is well known, the sexual 

 hormone which is administered directly, affects the uterus. 



